Plasma reactor having a symmetric parallel conductor coil antenna

Abstract

The invention in one embodiment is realized in a plasma reactor for processing a semiconductor workpiece. The reactor includes a vacuum chamber having a side wall and a ceiling, a workpiece support pedestal within the chamber and generally facing the ceiling, a gas inlet capable of supplying a process gas into the chamber and a solenoidal interleaved parallel conductor coil antenna overlying the ceiling and including a first plurality conductors wound about an axis of symmetry generally perpendicular to the ceiling in respective concentric helical solenoids of at least nearly uniform lateral displacements from the axis of symmetry, each helical solenoid being offset from the other helical solenoids in a direction parallel to the axis of symmetry. An RF plasma source power supply is connected across each of the plural conductors.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This is a divisional of U.S. application Ser. No. 09 / 611,169, filed Jul. 6, 2000, now U.S. Pat. No. 6,685,798, entitled “A PLASMA REACTOR HAVING A SYMMETRICAL PARALLEL CONDUCTOR COIL ANTENNA”, by John Holland, et al. and assigned to the present assignee.[0002]The following application / patents contain subject matter related to the present invention:[0003]U.S. patent application Ser. No. 09 / 611,170, filed Jul. 6, 2000, entitled “A PLASMA REACTOR HAVING A SYMMETRIC PARALLEL CONDUCTOR COIL ANTENNA”, by John Holland, et al.; U.S. Pat. No. 6,409,933, issued Jun. 25, 2002, entitled “A PLASMA REACTOR HAVING A SYMMETRICAL PARALLEL CONDUCTOR COIL ANTENNA”, by John Holland, et al.; U.S. Pat. No. 6,414,648, issued Jun. 11, 2002, entitled “A PLASMA REACTOR HAVING A SYMMETRICAL PARALLEL CONDUCTOR COIL ANTENNA”, by John Holland, et al.; U.S. Pat. No. 6,462,481, issued Oct. 8, 2002, entitled “A PLASMA REACTOR HAVING A SYMMETRIC PARALLEL CONDUCTOR COIL AN...

AI Technical Summary

Benefits of technology

[0015]The lateral displacements of the first plurality of conductors of the outer antenna preferably are uniform and the lateral displacements of the second plurality of conductors of the inner antenna preferably are uniform, whereby the inner and outer antennas are confined within respective narrow annuli of widths corresponding to the thickness of the conductors, whereby to maximize the differential effect of the inner and outer antennas on the radial distribution of applied RF field.

Problems solved by technology

One problem with such a coil antenna is that there is a relatively large voltage drop across the coil antenna, which can induce unfavorable effects in the plasma such as arcing.

Unfortunately, at such lower frequencies, the coupling of RF power to the plasma can be less efficient.

Another disadvantage of operating at the lower frequency range (e.g., 2 MHz) is that the component size of such elements as the impedance match network are much larger and therefore more cumbersome and costly.

Another problem with coil antennas is that efficient inductive coupling to the plasma is generally achieved by increasing the number of turns in the coil which creates a larger magnetic flux density.

This in turn leads to instabilities and difficulties in maintaining an impedance match over varying chamber conditions.

One limitation of coil antennas overlying the chamber ceiling (both conventional as well as the interleaved type) is that the mutual inductance between adjacent conductors in the antenna is generally in a horizontal direction generally orthogonal from the vertical direction in which RF power must be inductively coupled to the plasma.

This is one important factor that limits the spatial control of the power deposition to the plasma.

Thus, the ability to change the radial distribution of plasma ion distribution by changing the relative apportionment of applied RF power between the inner and outer antennas is limited.

This problem is particularly significant in processing semiconductor wafers with larger diameters (e.g., 300 mm).

This is because as the wafer size increases, it becomes more difficult to maintain a uniform plasma ion density across the entire wafer surface.

Another problem encountered with the use of inner and outer coil antennas is that the outer antenna typically has a significantly greater inductance than the inner antenna (because of the longer distances at the outer radii), so that they have vastly different impedances.

This problem is more acute as the chamber size increases to accommodate the trend toward larger semiconductor wafers.

However, another problem arises in that it is difficult or impractical to keep the two independent power sources in phase, so that undesirable effects arise due to the occurrence of constructive and destructive interference between the RF magnetic fields generated by the two antennas as their RF currents wander in and out of phase.

However, with such a single RF source, the disparity between the impedances of the inner and outer antennas is again a problem.

Images